A project I created several years ago does not have the TEST_HOST predefined that way. Yeah, same with us. It wasn't until I ran into trouble (see below), and tried swapping various settings to troubleshoot, that Xcode "updated" this use this new value: // Old BUNDLE_LOADER = "$(BUILT_PRODUCTS_DIR)/InternalName.app/InternalName"; TEST_HOST = "$(BUNDLE_LOADER)"; // New BUNDLE_LOADER = "$(TEST_HOST)"; TEST_HOST = "$(BUILT_PRODUCTS_DIR)/InternalName.app/$(BUNDLE_EXECUTABLE_FOLDER_PATH)/InternalName"; In our environment, with an iOS app, this value appears to be "". I can tell because we currently have a misconfiguration this is causing an error when trying to run our Tests: Could not find test host for Tests: TEST_HOST evaluates to "/Users/johnsmith/Library/Developer/Xcode/DerivedData/Internal-eaczvnalejwszegnxwnommslvcby/Build/Products/Production Configuration-iphonesimulator/InternalName.app/InternalName"